As usual, Twinkle is right. There is an overwhelming overpopuation of homeless animals today. The shelters and rescues are full up. Litters of kittens are all euthanized every day simply because there is no room. And the ones who are put to death are the lucky ones. Your male cat faces dangers outside every day, and since the mating drive is so strong, when he encounters other male cats, he faces dangers of attack and contracting diseases. I understand that some people insist cats need to be outdoors but to let an unaltered animal outside to breed is not responsible pet ownership. There are many low-cost (or free) spay/neuter programs and clinics today. PLEASE seek one out when and if he comes back and have him neutered.